On the bed there are two 0.69ohm resistors : one between 1 and 2 and one between 1 and 3. In 24V they’re connected in series and in the 12V configuration they’re connected in //. If you’re connecting 2 and 3 on the bed there’s only half the current going through the bridge. One single wire is enough here. But you must use two wires from 1 to terminal 1 of the SSR and 2 from either 2 or 3 to terminal 2 of the SSR.
So your solution is correct : one wire on 2 and one on 3 and both ending on terminal 2 of the SSR. No need to bridge 2 and 3 on the bed then.

[quote]I bought and assembled a heatbed from Marlark earlier. I was not shure about the electronics - I mean how to fix it - but with some help from Marlark I managed and made an instruction to do this: Vertex custom heatbed for dummies. Including 4 associated parts to print. This instruction also shows how to make the heatbed as a building platform.
Download the pdf [color=#FF4000]version v3[/color]: https://dl.dropbox.com/s/gsx5zu130azuno5/heatbed-for-dummies-v3.pdf?dl=0
If you would like to have a heatbed in your Vertex, don’t hesitate, it’s possible…[/quote]

Thanks for this guide svdv. In the guide, I see that you use some bolts with plastic “heads”? Or are they some kind of special washers? Where could one get those? Or should I just glue bolts with metal heads directly to the bottom of heated bed?

By accident I had some special plastic washers to use as a nice finish. You don’t need them.

Thanks for the reply. These washers ( or bushings, what is the correct term ? ) seem to be nice for taking the pressure from the springs, so that the bolts wont pop off from heated bed. I guess my way forward would be to glue the bolts, then print those things with ABS, add them to bolts and then move to using springs.
Do you know what the max temp tolerance for the glue should be?

That should be good up to 40A and thats well over the 23A the heatbed is taking at 15v and see how this will work out, because at the moment buying another psu and new cables and all is out of the
question at this point from the budget side of things and i dont really want 2 powersupplys hanging under my printer.

Still a SSR-40DD Relay should be a good replacement for the powerexpander, we will see how it goes.

Meanwhile i think i will order a new power expander as a backup plan if i consider switching to a 24v powersupply.

I’m not specialist in electronics, so I’ll drop this question here. Why it would be bad idea to use cheap electromagnetic relay ( With diode for reverse polarity protection ) to switch the heatbed?

I think its a good Idea but the relay has to fit the specifications, and the one, someone tested in here was a relay set for max of 25A which can be a little shortsighted considering the headbed draws about 23A at 15V so it could get quite warm, so i opted to buy the 40A one which should be more then enough for the heatbed.